1. Field of the Invention
The present invention relates to new oligourethanes which are stable in storage at room temperature and self cross-linking at elevated temperatures or which can be cross-linked with organic polyisocyanates optionally having masked isocyanate groups, the oligourethanes having reversibly blocked amino groups attached through urethane groups. The present invention additionally relates to a process for the preparation of these oligourethanes by the reaction of organic polyisocyanates, in which some of the isocyanate groups are optionally masked, with monohydric or higher hydric alcohols containing reversibly blocked amino groups, and their use as binders or binder components.
2. Description of the Prior Art
Compounds containing reversibly blocked amino groups used as reactants for organic polyisocyanates containing optionally masked isocyanate groups are already known. Thus for example, DE-AS U.S. Pat. No.1,520,139 describes heat cross-linkable two-component systems which can be cured to form polyureas and in which one component contains free isocyanate groups while the other component contains reversibly blocked amino groups in the form of aldimine or ketimine groups. DE-AS U.S. Pat. No. 1,694,237 describes heat cross-linkable combinations of isocyanate prepolymers containing isocyanate groups masked with phenol groups, and aliphatic or aromatic compounds containing ketamine and/or enamine groups.
It is now surprisingly been found that certain tertiary amines which will be described below, obtained by the Michael additive of secondary amines to certain acrylic acid derivatives, also constitute masked secondary amines which may be mixed at room temperature with polyisocyanates containing masked and/or free isocyanate groups. The masked secondary amines react with these polyisocyanates at moderately elevated temperatures of about 90.degree.-130.degree. C. with urea formation and, as opposed to the prior processes, the presence of atmospheric moisture is not necessary. Furthermore, free and/or masked isocyanate groups can easily be built into these new, blocked secondary amines to form storage stable systems which can undergo self cross-linking when heated to moderately elevated temperatures of about 90.degree.-130.degree. C.